Legislation pending in Sacramento would set up a hotline for motorists to report solo drivers who shave time off their commutes by sliding illegally into the diamond lane. Warning letters would be sent to registered owners of the offending cars and, while no ticket could be issued, officials hope the warnings will shame cheaters into following the rules of the road.

“This is a huge problem I hear about all the time in e-mails and letters,” said state Sen. Abel Maldonado, R-San Luis Obispo, who wrote the bill and represents the 15th District that covers towns such as Morgan Hill, Los Gatos and Saratoga. He said he’s followed commuter complaints in the Mercury News and listened to voters who say enough’s enough.

“We’re hoping once people receive a letter from a state agency and hearthe ramifications, they’ll follow the law. What we’re doing now is not enough.”

The hotline would probably follow a Seattle model, which since 1984 has used a statewide toll-free number (in Seattle, the last four digits are HERO). The first time an ineligible solo driver is reported driving in the carpool lane, the car’s owner is sent an educational brochure. More reports result in letters from the Washington Highway Patrol, which uses the information to pick areas to look for carpool cheaters.

Washington state officials believe the warnings work, saying less than 7 percent of the complaints they receive are about repeat offenders.

Although the national average for carpool cheating is between 10 percent and 15 percent, it’s less than 5 percent in Washington.

How many solo drivers cheat in the Bay Area is not clear. Caltrans studies indicate that fewer than four of every 100 drivers on roads like Highway 85 flout carpool laws. A Mercury News survey around Union Avenue four years ago yielded an average violation rate of 9 percent, nearly triple the state’s estimate of 3.4 percent in that area.

This much is known: Commuters think cheating is rampant. A recent University of California-Berkeley study says there are enough scofflaws to significantly slow speeds in the diamond lane by constantly dashing in and out of thick traffic. And the number of drivers ticketed in the Bay Area for $330-plus carpool violations is on the rise, from 18,035 in 2005 to 20,266 last year.

Milpitas banker Matthew Hawley drives alone on Highway 237 to Palo Alto each day and is “sick and tired of seeing carpool cheaters zoom by.”

Last week was the topper. Four times within five minutes, Hawley said, cheaters slowed to a near stop in the middle lane, blocking traffic for miles as they waited to enter the carpool lane.

“Four,” Hawley roared. “One right after the other, within about five minutes. And none were hybrids.”

Solo drivers of hybrids like the Toyota Prius and Honda Civic can drive in the carpool lane with proper stickers. Ditto solo motorists in electric cars and those running on natural gas, as well as some taxi drivers making runs to pick up those with disabilities or who are elderly.

Children count, too. All of which can make picking out cheaters harder than it looks.

“I don’t think cheating is as much as some people perceive,” said Sgt. Les Bishop of the California Highway Patrol. “I don’t know how many times I’ll pull a car over and think for sure I’ve got a solo driver in the HOV lane. Then I’ll either find someone asleep in the passenger seat or a child or baby I could not see.”

Not every commuter thinks a hotline is a good idea.

Callers would need to write down the license plate number, and it would be helpful to note the time of day, the highway and make of car. That means the callers need to take their eyes off the road.

“Or I would have to have photographic memory,” said James Kotsubo of Sunnyvale. “While I agree that carpool lane cheating is very rampant, especially since I see it everyday on 101, it might be more dangerous to write down their license plate numbers and potentially cause a car accident.”

The Bay Area already has one driver hotline, where people can report smoggy cars. The (800) EXHAUST line has met with moderate success. Of the estimated 32,244 complaints reported in 2005, the air district sent out about 11,000 letters to drivers.

One in four of those – about 2,800 – acknowledged that they had received the warnings, and many of them promised to repair or sell their smoking cars or asked about the region’s buyback program. As for the rest, officials don’t follow up with those who receive warnings, so it’s unclear whether the letters have the desired effect.

But if the carpool cheating hotline becomes operational, motorist Mark Costa of Menlo Park thinks it can work.

“I’d put it and 1 (800) EXHAUST on speed dial,” he said. “There’s huge, untapped power in shame. Letting folks know they’ve been caught would strike a delicious moment of fear when they open that letter.”

Do carpool cheats irritate you? Or is cheating not as widespread as some claim? Contact Gary Richards at mrroadshow@mercurynews.com or (408)920-5335.

Gary Richards has covered traffic and transportation in the Bay Area as Mr. Roadshow since 1992. Prior to that he was an assistant sports editor at the paper from 1984-1987. He started his journalism career as a sports editor in Iowa in 1975.